Personal computers currently used wide spread are equipped with a display which provide two dimensional images. However, computers of the future stay before a great challenge in terms of displaying three dimensional images. There already exist computer displays on the market, which are capable of visualizing a virtual three dimensional space. Amongst these there are displays that comprise a screen manufactured by high-end technology, which allow sensing three dimensional images without any auxiliary device, whilst there are much cheaper displays as well, which typically provide the three dimensional view by using special glasses. That purpose of the application of a computer is not only visualizing information but also inputting, and processing information, in relation to computers adapted to display three dimensional images, and a need has been arisen for inputting and processing spatial information, that is for performing operations in the virtual three dimensional space. Although several companies offer computer systems designed for visualizing a virtual three dimensional space, said computer systems being principally available for everyday use at home, 3D technologies applied therein have either very limited capabilities or they are very expensive, and that is why such systems have not used wide spread for the time being. Hereinafter, some of the prior art devices and systems are briefly introduced that are capable of visualizing a virtual three dimensional space and allow performing operations therein.
In the foregoing and the following part of the description, the term “3D space” is used for a well defined segment of the space, that is the term “real 3D space” means a segment of the real space for locating the position of an operation to be performed by moving a positioning device, whereas the term “virtual 3D space” means a segment of a space visualized by a 3D visualizing means.
Document DE 10106850 A1 discloses a position tracking system for 3D computer applications, wherein the position tracking system comprises a spatially movable positioning device, the motion of which is mapped into the virtual three dimensional space. The positioning device is coupled by springs to linear rails arranged orthogonally to each other, said rails representing a spatial coordinate system. The spatial location of the positioning device is detected by a potentiometer system. In this position tracking system, a spatial position is detected by means of a mechanical assembly, which makes actuation of the positioning device more difficult and strongly limits the size of the space segment available for locating the position of an operation.
An even more flexible position tracking system is disclosed in document GB 2388418 A, wherein the position tracking system, the operation of which is based on optical principles, comprises a three dimensional object, for example a cube or a ball, as a positioning device, said object being adapted for moving by hands freely. The image of the object is recorded by a camera. Changes in the spatial position and the orientation of the positioning device are determined from the two dimensional images recorded by the camera. Although use of a second camera is also mentioned in this document, the function of this additional camera is merely limited to obtain supplementary information from eclipsed or awkwardly lit parts of the positioning device. A further disadvantage of this system is that the virtual space is not calibrated to the real-space, therefore the positioning device can be used only for locating relative positions.
A similar solution is introduced in document WO 03/079179 A1, which discloses a positioning device as a spatially movable embodiment of a conventional computer mouse. Such a so called space mouse is provided with a plurality of light sources and a plurality of micro-switches, wherein the light sources may have different colors, sizes or shapes so that the camera can sense displacement or rotation of the space mouse in every spatial direction. Although the above space mouse allows very flexible positioning, its manufacturing cost is rather high.
The purpose of the three dimensional visualization is to provide the capability of sensing spatial shapes as reality by human beings. The spatial effect may be achieved by conveying different images to the left eye and the right eye as the eyes themselves do sense the spatial shapes from different positions. For generating and sensing such a double or stereo image, several technologies have been developed. In the simplest case, the stereo image for the two eyes is displayed on a conventional screen simultaneously and the spatial effect can be sensed by means of special glasses. However, there are sophisticated and very expensive displays as well, which do not need the use of such glasses or any other auxiliary device, since the screen itself provides the stereoscopic view.
One of the simplest and most wide spread solution is based on the separation of two images presented on the same place. In such systems, images for the left and the right eye are displayed on the screen at the same time, and the two images are separated by special 3D glasses in such a way that only the images for the left eye are allowed to pass through the left lens, while only the images for the right eye are allowed to pass through the right lens. Now we introduce some of the systems operating on the basis of image separation.
The core idea of the 3D visualization based on color separation is that two images of different color are generated for the left and the right eye, and the two images of different color are separated by coloured lens. For this purpose, a red lens and a cyan lens are generally used. Through the red lens, only red light can pass, while through the cyan lens, only cyan light can pass. The advantage of a color separation system is its low price, however, one drawback thereof is that it may be harmful for the eyes after a use of 10-15 minutes and another drawback is that it is not available for providing a color three dimensional view.
The core idea of the light polarizing systems is that differently polarized images are generated for the left and the right eye, and the two images of different polarity are separated by polarizing lenses. Unlike the color separation systems, color and entirely realistic images can be reproduced in a light polarizing system. Although manufacturing costs of such polarizing lenses are relatively low, the display device for reproducing the stereo image consisting of images polarized in two directions is very expensive, thus this solution is mostly used in 3D movies.
The systems using so called shutter glasses operate in a manner that respective images for the left and the right eye are displayed alternately, and a pair of shutter glasses do the job of alternately eclipsing one eye after the other, synchronously with the display device. Shutter glasses have lenses adapted to switch between an opaque state and a transparent state at a high frequency. Similar to a light polarizing system, a shuttering system is also available for reproducing color and entirely realistic images. Such a system is advantageous due to its relatively low price and to the fact that unlike a light polarizing system, a conventional computer display is enough to use therein.
A common issue of the above mentioned 3D visualizing systems that they cannot detect and thus cannot follow the position of the eyes, i.e. the view point of the user. Consequently, if one moves away from the optimal position providing the three dimensional effect, the virtual objects will shift in the virtual space and they will appear with more or less distortion, which will lead to a degradation of the realistic impression of the three dimensional image. This problem may be avoided by using a head mounted display (HMD).
A HMD display is a special pair of glasses which comprises two displays of reduced size in place of the lenses, said displays directly reproducing the respective images for the two eyes. HMD displays are provided with magnetic and gravitational sensors for sensing any motion of the head, therefore they reproduce undistorted images even if the user is moving and in addition, they are adapted to work even with a 360 degree turn-around of the user. Disadvantages of the HMD displays include their high price due to the special sensors and their limited capability of displaying only a narrow angle of sight of approximately 30-40 degrees.
Systems for performing operations in the virtual three dimensional space are addressed to allow various activities in the virtual space for the user so that operations are performed at locations in the virtual space corresponding to locations selected in the real space and in addition, the operations or the result of the operations can be sensed as reality with three dimensional effect. A common purpose of such systems is to allow performing operations within the virtual tree dimensional space, in addition to visualizing it.
One of the most known virtual 3D manipulation systems currently on the market is the Reachin Core from Reachin Technologies AB, which comprises a special application level programming interface and an integrated 3D position tracking and 3D visualizing system. For the spatial operations, the Rachin Core uses a three dimensional marker developed by SensAble Inc., the position of which is tracked by the computer by means of a mechanical system. The marker is fixed to the end of mechanic arms, and the position of the marker is determined from the inclination angles of the hinge joints of the arms. There is also provided a push button on the marker, the function of which is similar to that of a mouse button. One of the advantages of this kind of marker is that any operation can be freely performed with it in three dimensions in the same manner as with a conventional computer mouse in two dimensions. Furthermore, the marker is provided with a force-feedback mechanism, thus virtual objects become tangible in fact. Such a virtual 3D manipulation system allows to bring the place of the real spatial operation and the place of its virtual three dimensional appearance into coincidence. The three dimensional image can be sensed by using a pair of shutter glasses and a mirror, wherein the three dimensional image appears behind the mirror. The marker is also used behind the mirror, thus the place of the activity and the place of the reproduced image is the same. A drawback of this system is that the real space and the virtual space is not perfectly coincident, since the position of the shutter glasses is not being tracked and therefore the reproduced image cannot be properly oriented with respect to the position of the eyes, i.e. to the view point of the user. The same problem arises in all the other virtual 3D manipulating systems existing currently on the market.